Method and apparatus for irrigating container-grown plants

ABSTRACT

The subirrigation of soil in a container for container-grown plants is accomplished upwardly through an opening in the container bottom by placing the container on the upper surface of a capillary sheet in the form of a sheet wettable plastic having a multiplicity of capillary openings therein and by disposing the capillary sheet so that its undersurface directly overlies in unbonded face-to-face contacting relation an essentially continuous and substantially smooth wettable surface presented by a substantially flat member comprised in a support bed for the container as, for example, by a sheet of plastic overlying a substantially rigid member or by a substantially rigid slab comprised in the support bed and feeding an aqueous liquid into the interface between said surfaces as through feeder tubes by gravity or by capillary travel from a reservoir disposed below the interface, whereby the so fed aqueous liquid becomes distributed by capillary action to any portion of the capillary sheet directly underlying a plant container resting thereon and then upwardly through the openings in the capillary sheet and into the soil in the container. Other features relate to a duplex supporting tray for plant containers to be irrigated that comprises an upper tray on which plants may be irrigated as described above and a lower tray into which liquid may drain from the upper tray and from which, when required, liquid may be drawn upwardly by a capillary wicking action to irrigate soil in containers supported by the upper tray.

FIELD OF THE INVENTION

This invention relates to the irrigation of soil or other growing mediumfor plants and relates more especially to the irrigation of bodies ofsoil in conventional plant containers therefor appropriate for plantculture in greenhouses, florist shops, residences, offices and the like.

BACKGROUND OF THE INVENTION

The proper irrigation of soil or other plant growing medium is importantin achieving optimal conditions for successful plant culture. In my U.S.Pat. Nos. 3,220,144 and 3,193,970 apparatus is disclosed for providingcontrol and regulation of water appropriate in the case of a singleplant. In my U.S. Pat. No. 3,778,928 an irrigation system is disclosedappropriate for controlling irrigation to a plurality of plants inindividual containers disposed on a common support such as a bench usedin a greenhouse. In my U.S. Pat. No. 4,001,968 I disclose a furtherimprovement in a system for the subirrigation of soil in plantcontainers characterized by the employment of a capillary sheet having amultiplicity of substantially evenly spaced capillary openings thereinoverlying a water receptive material which preferably is in the form ofthe silica sand catalyst sheet that is more particularly described insaid U.S. Pat. No. 4,001,968 and that is characterized by a plasticsheet having an adherent continuous coating approximately 1 grain inthickness of silica sand particles essentially in the range from about0.002 mm to about 0.25 mm that are interspersed with a network ofcapillary spaces conducive to lateral spreading of water therealong.Conditions providing excellent results in accomplishing subirrigationare afforded by the method and means disclosed in my U.S. Pat. No.4,001,968. However, in order to attain the advantage of the silica sandcatalyst sheet described in my patent the sheet must be manufactured bythe application of the silica sand particles to an adhesive surfacepresented by a plastic sheet. This requires the use of apparatusappropriate for the purpose and the supply of silica sand particleshaving the requisite dimensional characteristics. Accordingly, thesilica sand catalyst sheet contributes significantly to the overallexpense of an installation utilizing and comprising the subirrigationsystem disclosed in my U.S. Pat. No. 4,001,968.

It is an object of this invention to provide a subirrigation system andmethod which successfully provides water to soil in plant containersresting on the capillary sheet hereinabove referred to without theemployment of the silica sand catalyst sheet for accomplishing capillarytravel under the capillary sheet into the area of the capillary sheet incontact with the bottom of a plant container.

It is a further object of this invention to provide a subirrigationsystem which can be successfully employed and which may be affordedwithout the expense incident to the preliminary formation of the silicasand catalyst sheet.

Further objects of this invention relate to the provision of an improvedtray for supporting plant containers for accomplishing subirrigationwhich utilizes the improvement of this invention and also is of improveddual bottom construction.

GENERAL STATEMENT OF THE INVENTION

As a result of my continuing research activities I have found that theaforesaid objectives of this invention may be realized in a surprisingmanner merely by introducing an aqueous liquid into the interfacebetween the undersurface of a capillary sheet of the character aforesaidthat presents a wetable undersurface and an essentially continuous and asubstantially smooth wettable surface presented by a support bed forsupporting plant containers to be irrigated such as the surfacepresented by a conventional sheet of plastic or by the surface of arigid supporting bed. In the latter case all that is required is tospread the capillary sheet directly over the smooth surface of theunderlying rigid bed. The water may be water as conventionally availableor may contain a suitable amount of plant nutrient. Hereinafter and inthe claims the aqueous liquid is referred to as water with theunderstanding that the water may contain plant nutrients. When theundersurface of the capillary sheet and the surface presented by thesupport bed are in face-to-face unbonded contacting relation and arewettable with the water I have found that the water becomes laterallydistributed about the interface between them by capillary action in anamount that is amply sufficient to provide the necessary moisture forsoil contained in a plant container which rests on the capillary sheet.Of course, the plant container should have at least one opening in thebottom thereof such as the usual drain opening that is conventionallyemployed in containers for soil in which plants may be grown. Water maybe fed into the interface from a reservoir which is at a level above thelevel of the support bed. Moreover, if the aforesaid interface is incommunication with a wick extending down into an underlying waterreservoir water becomes carried upwardly into and throughout saidinterface and then travels through the capillary openings underlying thebottom of a plant container resting on the capillary sheet followed bycontinued upward travel into the soil. In order to provide communicationbetween the upper surface of the capillary sheet and soil in thecontainer that rests on the capillary sheet, one can employ a length ofwick material which passes through an opening in the bottom of thecontainer so as to make contact with the upper surface of the capillarysheet and extends a substantial distance up into the soil in thecontainer. Preferably this wick is made of the above-mentioned silicasand catalyst sheet which is fashioned so that the silica sand catalystsheet will be in direct contact with the upper surface of the capillarysheet and extend therefrom up into the soil in the plant container sincethe silica sand catalyst sheet exercises a very desirable and effectivewicking action. While a wick may be employed I have also found that ifthe bottom of the container is flat so that substantially the entirearea of the bottom of the container is in direct contact with thecapillary sheet moisture will effectively migrate from the capillarysheet up into soil in the container even though no wick is employed.

This invention is excellently adapted for use by professional growers ingreenhouses where the benches for growing potted plants are ofsubstantial size. Since the plant supporting bed comprised in agreenhouse bench usually is somewhat even the smooth upper surfacepresented by the support bed is provided by a sheet of wettable plasticthat is spread over the support bed of the greenhouse bench. The plasticcapillary sheet is then spread over the top of the continuous sheet ofplastic and suitable means is provided for gradually feeding water intothe interface between the two sheets.

It is an additional feature of this invention that when a subirrigationsystem is afforded in the manner described any excess water may be takenoff through a drain line and recirculated to a sump from which it may bepumped back into a reservoir for supplying water into the region of theinterface between the two sheets. By this measure the amount of water isvery substantially reduced since the amount of makeup water that isrequired from an outside source is relatively small. The simplicity ofthe construction is such that the support bed used for supporting thepotted plants in greenhouses may be of any convenient size. Thus whilethe support bed may be only 3 or 4 feet wide and 6 feet long it also ispossible to provide a support bed of substantially greater extent suchas several hundred feet from end-to-end and about 6 feet or more wide.In such case a plurality of feed lines may be provided for feedingliquid at appropriate intervals into the interface underlying thecapillary sheet.

Installations embodying the present invention that have been used inmajor experimental installations have been found to be extremelysuccessful in the growing of a number of different plants including notonly flowering plants such as poinsettias, roses and the like, but alsogarden plants such as tomato plants. Considerable difficulty has beenexperienced in the past in producing greenhouse grown tomatoes whichhave the desirable characteristics of outdoor grown tomatoes. By use ofthe subirrigation system of this invention tomato plants have been grownthat have produced an abundance of tomatoes which are comparable tothose produced by outdoor grown plants.

While this invention is highly desirable for use in greenhouses, it alsolends itself to the provision of smaller trays used for supportingpotted plants that may be used in residences and in small conservatoriessuch as those used for growing plants as a hobby. Certain features ofthis invention relate to the construction of such trays. In the case ofa relatively small size tray the interface into which the water issupplied may be provided between the undersurface of the capillary sheetand a smooth wettable surface presented by the rigid substantially flattray bottom. A relatively small tray appropriate for growing pottedplants, unlike a greenhouse bench, may be produced with a substantiallycontinuous and smooth upper surface which is wettable and which maydirectly underlie the capillary sheet. In such case water fed into theinterface between the capillary sheet and the upper surface of the rigidtray bottom will become distributed laterally as hereinabove describedfor accomplishing irrigation of the potted plants by travel through thecapillary openings and thence into the soil in the plant container.

It is a further feature of this invention that a tray essentially asherein described may be used in combination with an underlying traywhich supports the upper tray with its undersurface in adjacent spacedrelation to the upper surface of the lower tray so as to provide aduplex tray. When this combination is employed water may be introducedinto the interface between the undersurface of the capillary sheet andthe supporting surface comprised in the upper tray which supportingsurface may be presented either by a sheet of substantially smoothwettable plastic or, preferably, the upper wettable surface of the rigidslab comprised in the tray bottom from a reservoir from which water maybe gradually fed so to flow into the interface for lateral distributionwith drainage of any excess water into the underlying tray which servesas a second reservoir. When the water in the first reservoir isexhausted water from the second reservoir provided by the underlyingtray is fed back up into the interface by the use of a wicking meanswhich preferably is in the form of a piece of the silica sand catalystsheet, e.g., in the form of a tube which extends from the aforesaidinterface to the bottom of the underlying tray. However, any otherconventional wicking materials such that commonly are sold with pot andsaucer combinations for house plants may be employed. When thisconstruction is employed, it is possible to introduce water initiallyinto the underlying tray. However, it is preferable that the water beinitially supplied from a reservoir so that it will feed by gravity intothe interface with an excess draining into the lower tray as hereinabovedescribed.

As described in my U.S. Pat. No. 4,001,968, the capillary sheet that isused is one that is impervious to moisture and that preferably is opaqueand comprises a multiplicity of openings for capillary flow therethroughas described more fully in said patent. The material out of which thecapillary sheet may be made is also fully described in my U.S. Pat. No.4,001,968 and as described in said patent ordinarily is in the form ofpolyethylene sheet material such as that which is conventionallyavailable in the form of a continuous sheet. The thickness of the sheetmaterial is not critical. Thus good results are obtained from the use ofindividual sheets the thickness of which is of the order of 11/2 mils,or 2 mils. Undesirable growth of algae is minimized by using a capillarysheet that is opaque. In the usual case it is black. The capillaryopenings may be produced by passing the plastic sheet from an unwindroll to a wind-up roll between which there is a pair of rolls that thesheet passes between, one of the rolls presenting a multiplicity ofprojecting prongs and the other roll presenting a yieldable surface suchthat the prongs may pass through the sheet material and may be withdrawnagain during travel of the sheet through the nip between the rolls.Capillary openings having desirable functional utility for capillaryflow may be produced by using prongs the diameters of which are about0.045 inch. The spacings between openings in the capillary sheet for allpractical purposes are regularly or evenly spaced approximately 1/2 inchapart. During the process of making the capillary holes the prongs willrip holes larger than 0.045 inch but resealing under use will reducetheir size to approximately 0.045 inch. The spacing of about 1/2 inch isordinarily employed and the plastic sheet is about 1.5 mils inthickness. In the case of sheets of greater thickness the holes may bemore closely spaced so as to run about 1/4 to 1/8 inch from each otheron the average or somewhat greater than 1/2 inch for use with largeplants. The diameter of the capillary openings in the capillary sheetmay vary considerably but essentially should be in the range from about0.05 to about 0.15 inch.

As described more fully in my U.S. Pat. No. 4,001,968 the silica sandcatalyst sheet material when used preferably is made utilizing a vinylbase sheet. By applying a conventional solvent to the surface of thevinyl sheet it can be rendered sufficiently sticky before the solventevaporates to cause the silica sand to adhere thereto as a thin layer.Alternatively a polyethylene sheet may be used and by applying aconventional water-resistant adhesive that is sticky prior to drying thesand particles can be caused by stick thereto. As aforesaid the silicasand is applied as a thin coating with the sand particles sufficientlyclosely spaced to provide a network of capillary spaces conducive tolateral spread of water therealong. If the sand layer is substantiallythicker than single grain thickness, the sand tends to hold water in aform that may be likened to an absorbant gel which is undesirable astending to the creation of anaerobic conditions. When the silica sand isessentially of the order of a single grain in thickness the conditionsare very favorable to the maintenance of aerobic conditions. Preferablythe sand that is employed is one which is somewhat windblown and of thesize hereinabove mentioned.

In those modifications of this invention wherein a silica sand catalystsheet is used, as for example a wick because of its wicking action, thisis regarded as desirable inasmuch as the silica sand catalyst isbelieved to exercise a catalytic effect in stimulating plant growth whenmoisture containing nutrient is exposed thereto in its travel to theroots of a growing plant. It is one of the advantages of this inventionthat it lends itself very well to the supply of a plant nutrientcontained in the water that is used for supplying moisture since thewater is taken up from the bottom into the plant container and the plantnutrient therein is efficiently used without risk of washing it out ofthe container as is the case when the soil in the plant container iswatered from the upper surface. This preferable utilization of nutrientalso may be realized by the use of wicks made from other materials butfor the reasons abovementioned when a wicking action is utilized it ispreferable that the wicking action be accomplished by the use of thesilica sand catalyst sheet which can be used double to get good contactsfrom capillary sheet to soil in container.

Further purposes, features and advantages as well as more detaileddescriptions are set forth hereinafter in connection with theaccompanying drawings which are intended to be illustrative of thepractice of this invention without, however, limiting the scope of thisinvention, wherein,

FIG. 1 is a perspective view of an irrigation system embodying thisinvention wherein the support bed for the plant containers is providedby a greenhouse bench or pallet;

FIG. 2 is a sectional elevation of the system shown in FIG. 1 on anenlarged scale and with an intermediate portion thereof broken away;

FIG. 3 is a sectional elevation illustrating the employment of thisinvention as embodied in a duplex tray for use in cultivatingcontainer-grown plants, a central portion of the tray being broken away;

FIG. 4 is a sectional elevation showing an end portion of a duplex traywhich is similar to that shown in FIG. 3 but which is illustrative of adifferent embodiment of the invention;

FIG. 5 is similar to FIG. 4 and illustrates a still further embodiment;

FIG. 6 is a view from below of the bottom of the flat bottom plantcontainer shown in FIG. 5;

FIG. 7 is a perspective view of the silica sand capillary sheet used asa wick in one type of plant container, the capillary sheet is eitherdoubled or sanded on both sides to provide contact;

FIG. 8 is a perspective view of the silica sand catalyst wick used inthe duplex tray of FIGS. 3, 4 and 5; and

FIG. 9 is a sectional elevation of another embodiment.

With particular reference to FIGS. 1 and 2 a support bed forcontainer-grown plants is shown in the form of a pallet which isindicated generally by the reference character 10. By way of example thepallet may be in the form of a panel of 3/4 inch all weather plywood 11which, if desired, may be provided with stiffening strips underneath(not shown). A sheet of conventional polyethylene plastic 12 is spreadover the upper surface of the pallet or panel 10. The polyethylene sheetmay be from about 0.004 to about 0.006 mils in thickness and preferablyis substantially opaque. Such sheets of polyethylene are commonlymanufactured in the form of a continuous roll. The surface of the sheetis substantially smooth and the material is such that the surface iswettable. In other words when moistened with water the water tends towet the surface as distinguished from being repelled from the surface aswould be the case if the surface of the sheet were to be covered with afilm of oil. After the sheet of polyethylene plastic has been spreadover the surface of the pallet a support bed is thereby provided whereinits upper surface is the smooth wettable surface of the plastic sheetthat rests on the underlying substantially rigid slab of plywood orother structural material. This essentially continuous sheet of plasticpreferably is opaque.

The capillary sheet 13 is next spread over the surface of the plasticsheet 12 with its undersurface in unbound direct face-to-face contactwith the upper surface of the sheet 12. The surfaces of the capillarysheet also are wettable. Water may be fed into the interface betweenthese two sheets in any desirable way. In the illustrative embodimentshown, a body of water 14 in a reservoir 15 is taken therefrom by aconduit 16 with which leader tubes 17 are connected at appropriateintervals for feeding water gradually into the interface between the twosheets. While in FIGS. 1 and 2 a pallet is shown which may be of theorder of 3 or 4 feet×8 feet, it is to be understood that there may be asuccession of contacting support pallets or, alternatively, there may beone continuous bench which may be of extensive extent and which atappropriate intervals can be fed with water from extensions of theconduit 16 having leader tubes 17 communicating therewith.

While the irrigation system may be employed merely by introduction ofwater into the interface between the continuous plastic sheet and theoverlying capillary sheet under conditions such that any water is merelydrained onto the ground, it is a further feature of this invention thatthe supply of water may be conserved by providing drain means as shownby the drain line 18. While only one drain line is shown in the drawing,it is to be understood that depending on the extent of the support bedadditional drain lines may be provided at appropriate intervals. Toassist the flow of any excess water into the drain line the margin ofthe support bed preferably is provided with a border strip 19 which, forexample, may be about 1/4 inch in thickness and about 1 inch in width.For the purpose of conserving the supply of water, particularly when itis regarded as advantageous to fortify the water that is used with asmall amount of plant nutrient, the drained water may be directed intothe sump 20 through the line 20A. The sump is provided with a pump 21which when necessary becomes effective to pump the water through thereturn duct 22 for re-introduction into the reservoir 15. Of course, acertain amount of the water is taken up into the plant containers and byevaporation is taken up by plants growing therein with the result that acertain amount of makeup water is supplied to the water in the reservoir15 as, for example, by the use of a float valve 23 which controls theinflow of fresh water from the supply line 24. It is a standard practiceto chemically reconstruct recycling drainage to plants' requirement.

As shown particularly to FIG. 1 and also in FIG. 2, containers in whichplants are being grown may be placed in any position on the uppersurface of the capillary sheet. It has been found as a result ofrepeated experimental tests that in such case the water will travellaterally by capillary action between the two sheets to those areas ofthe capillary sheet which make contact with the bottom of the severalplant containers. In those areas the water has been found to travelupwardly through the openings of the capillary sheet and into the soilin the container so as to supply the root system of a plant being grownin the container with an adequate supply of moisture under conditionssuch that the supply of water is regulated in a controlled manner.

It is apparent from the foregoing that subirrigation plant supportssuitable for use in greenhouses can be provided in a very inexpensivemanner when employing the improvements of the present invention. Allthat is required is a substantially flat support bed of one kind oranother and the spreading of the continuous plastic sheet so as tounderlie the capillary sheet. In order to assure the most effectivelateral capillary distribution it is especially important that theunderlying continuous plastic sheet presenting the smooth surface beessentially continuous. After the support bed has been provided in themanner described then means, such as that hereinabove described, may beprovided to feed water into the interface between the two sheets forsupplying moisture to plant containers which are supported by thesupport bed provided in the manner described.

In order to provide effective transmission of water from the uppersurface of the capillary sheet through an opening in the bottom of aplant container the bottom of the plant container may be made in eitherof two ways as is illustrated more particularly in connection with FIGS.3, 4 and 5 which are to be described. If the plant container is onewhich has projections from the bottom so as to make poor contact withthe capillary sheet, then it is desirable to provide a wick whichcontacts the capillary sheet and extends upwardly through an opening inthe bottom of the container into soil within the container. On the otherhand, if the bottom of the plant container is flat so as to make goodcontact throughout with the capillary sheet, then the employment of awick is unnecessary.

FIG. 3 illustrates that embodiment of this invention which comprises aduplex supporting tray. The use of such a supporting tray isparticularly advantageous when this invention is employed on a smallscale for growing potted plants in residences and conservatories bythose who grow plants in laboratory research and as a hobby. The traysmay be of any desired dimension but ordinarily do not exceed dimensionswhich would make handling of the trays inconvenient. In the embodimentshown there is an upper tray 25 which may be made of a suitablesubstantially rigid material such as plastic having a smooth uppersurface that is wettable. The upper surface of the tray 25 is directlycovered by the capillary sheet 26 which ordinarily has the same lateraldimensions as the bottom of the tray 25. As shown the under wettablesurface of the capillary sheet is in face-to-face unbonded contact withthe upper smooth wettable surface of the slab that forms the bottom ofthe tray 25. A small reservoir 27 is provided which contains water 28which preferably is fed into the interface between the capillary sheetand the surface of the tray through one or more leader tubes 29 whichpreferably are of such small internal diameter as to feed the water in agradual manner into the interface for lateral capillary distributionthroughout. Alternatively the water from reservoir 28 may be graduallyfed onto the upper surface of the capillary sheet so as to be dischargedunderneath the container 27 or other object resting on top of thecapillary sheet for capillary travel down into the interface where itbecomes laterally distributed.

The upper tray 25 is supported by the lower tray 30 so that the bottomof the upper tray is in adjacent spaced relation to the upper surface ofthe lower tray 30 by the legs 31 protruding from the bottom of the uppertray 25. There is a drain opening 32 in the bottom of the upper traythrough which any excess aqueous liquid may drain so as to accumulateand thereby provide a reservoir of liquid 33 which is stored in thebottom of the lower tray. In order that the liquid that is drained intothe lower tray may be utilized by plants being grown while supported bythe upper tray, a wick extends from adjacent the upper surface of thelower tray through the drain opening 32 and into the interface betweenthe capillary sheet and the upper surface of the bottom of the uppertray. In the embodiment shown this wicking action is provided by a tube34 of the silica sand catalyst sheet which per se is shown in FIG. 8.While the wicking action of the silica sand catalyst sheet is preferredfor the reasons hereinabove mentioned, other wick materials may be usedfor the purpose described. When the duplex support tray is provided inthe manner described, water will be directed from the reservoir 27 intothe interface between the upper surface of the bottom of the upper trayand the lower surface of the capillary sheet and after the water in thereservoir 27 has been exhausted the moisture in the region of theinterface will continue to be supplied by capillary action from theliquid 33 that has drained into the lower tray until this liquidlikewise has been exhausted.

The types of plant containers hereinabove referred to are shown in FIG.3. The container 35 is illustrative of a container which is providedwith a flat bottom for making contact substantially throughout with thecapillary sheet. When the container is made in this way a wick may bedispensed with. Preferably the flat bottom container that is usedwithout any wick is made with openings in the bottom that are somewhatlarger than those in the bottom of a conventional plant container. Theopening may be provided in various ways. FIG. 6 is illustrative ofsuitable openings in the bottom of a plant container. Preferably thetotal area that is open is at least about 30% and preferably 40% of thetotal area of the bottom of the container. While it is preferable thatthe openings be somewhat larger than conventional, plant containershaving bottom openings of conventional size also may be employed withexcellent results provided the container bottom is flat so as to makecontact substantially throughout with the upper surface of the capillarysheet. When a flat bottom container is used without any wick it normallyis desirable to initially jar the soil in the container down slightly soas to assure close proximity to the upper surface of the capillarysheet.

The container 36 in FIG. 3 is of the type which has protuberances 37from the bottom and when this type of plant container is used thewicking action into the soil in the plant container can be provided by awick 41 (see also FIG. 7) which makes contact with the capillary sheetand extends upwardly from an opening in the bottom of the container intosoil within the container. Preferably the wicking action is provided bya strip of the silica sand catalyst sheet which has ears 42 positionedso that the silica sand coating is in contact with the upper surface ofthe capillary sheet.

When a duplex tray is employed, as illustrated in FIG. 1, it isconvenient that a portion of the lower tray extend slightly beyond onemargin of the upper tray as indicated at 38 so that one may readilyobserve whether or not any aqueous liquid is present in the lower tray.

FIG. 4 is illustrative of an additional embodiment of the duplex trayshown in FIG. 3 wherein the different portions are indicated by likereference characters. In this modification a sheet of essentiallycontinuous wettable plastic 39 is initially spread over the bottom bedof the upper tray and the water is fed into the interface between theupper surface of the continuous plastic sheet and the lower surface ofthe overlying capillary sheet. This embodiment of the invention ismerely shown for the purpose of indicating that the duplex trayembodiment of the invention does not necessarily require that thecapillary sheet rest on the upper surface of the rigid bottom bed of theupper tray. When the upper surface of the rigid bottom bed is smooth andwettable, then the plastic sheet 39 preferably is omitted. However,there may be circumstances such that the presence of the plastic sheet39 may be desirable. In this connection it may be added that if in alarger installation appropriate for use in the greenhouse the uppersurface of the rigid support bed is sufficiently regular and issufficiently wettable, the plastic sheet 12 shown in FIGS. 1 and 2 maybe omitted and water may be fed into the interface that is formedbetween the upper surface of the underlying bed and the overlyingcapillary sheet. However, in most greenhouse installations thesupporting bed, is made of material such as plywood that is excessivelyabsorptive and therefore interferes with the lateral travel of the waterunderneath the capillary sheet. The surface that directly underlies thecapillary sheet should, in the practice of this invention, besubstantially impervious and this also applies to the capillary sheetitself except for the capillary openings therein. In the embodimentshown in FIG. 4, water from the reservoir 33 may be drawn up into theregion of the interface between the upper surface of the continuousplastic sheet 39 and the undersurface of the capillary sheet 26 by asuitable wick which preferably is afforded by a tube of the silica sandcatalyst sheet that is similar to that shown in FIG. 8 with the ears 43in the region of the interface occuring so as to directly underlie thecapillary sheet.

While it is not normal practice, one may gain the advantage of theduplex tray feature of this invention by substituting for the plasticsheet 39 a silica sand catalyst sheet as hereinabove described which hasthe surface presenting the silica sand layer in face-to-face contactingrelation with the underside of the overlying capillary sheet as also isdescribed in my U.S. Pat. No. 4,001,968. This embodiment of thisinvention is mentioned for the purpose of illustrating the fact that theinvention of my prior patent can lend itself to use with a duplex trayfor the purposes herein described. However, when the duplex tray isemployed, it is preferable in the interest of economy and convenience toemploy the embodiment of this invention shown in FIG. 3 wherein theunderside of the capillary sheet directly overlies the upper surface ofthe substantially rigid wettable slab which forms the bottom of theupper tray. The container 44 of FIG. 4 is similar to the container 36 ofFIG. 3.

The duplex tray combination shown in FIG. 5 is similar to that of FIG. 3and like parts are indicated by like reference characters. Theembodiment of FIG. 5 is illustrative of the preferred practice of thisinvention wherein a plurality of layers of the capillary sheet is used.In FIG. 5 the additional capillary sheet 45 underlies the uppermostcapillary sheet 26 and overlies in directly contacting relation to theupper surface of the bottom of the tray. One also may employ more thantwo layers of the capillary sheet. The use of a plurality of layers ofthe capillary sheet is especially desirable in the case of plants thatare left in the same position resting on the upper surface of theuppermost capillary sheet for a substantial period of time such as inthe growing of tomato plants or bringing young flowering plants tomaturity. Accordingly, it is to be understood that the term "capillarysheet" as used herein and in the claims has application not only to asingle capillary sheet but also to a capillary sheet in the form of aplurality of unbonded contacting layers of single or individual plasticsheets having capillary openings therein as hereinabove described. InFIG. 5 the container 47 is a flat bottom container similar to container35 shown in FIG. 3. The pattern and dimensions in the openings in thebottom of the flat container 47 are shown in FIG. 6. Particularly when acontainer having a flat bottom is used some roots of the plant growingin the container in seeking water extend into and spread out laterallyin the interface underlying the capillary sheet. This is beneficial infacilitating what is regarded as a plant respiratory action whereinwater containing nutrients is taken up by the plant roots while acertain amount of water from which nutrients have been removed whichcontain plant excrement is carried away. Different plant varieties havedifferent patterns as regards root depth and by employing a plurality ofcapillary sheets conditions are made more favorable with a greater rangefor growing plants to select preferred root depth. It would not beinconsistent with the practice of this invention when using anembodiment of this invention comprising a plurality of overlyingcapillary sheets to replace one of the capillary sheets other than thetopmost sheet with a sheet of felt or other wetable water absorptivematerial. The embodiment of FIG. 5 may be provided with a drain having asilica sand wicking tube 34 therein (not shown) in correspondence withthe drain 32 and silica sand wicking tube shown in FIG. 3.

A further duplex tray embodiment of this invention is shown in FIG. 9.The upper tray 48 and the lower tray 49 are identical. Each has anupstanding border rim 50 and a downwardly extending continuous ordiscontinuous strip 51 positioned and dimensioned so that the upper traymay be stacked above the lower tray with the bottom strip 51 of theupper tray contacting the upper surface of the lower tray and with theundersurface of the upper tray spaced substantially from the uppersurface of the lower tray. Adjacent each end of the upper tray there isa drain opening 52. The upper surface of the upper tray is wettable andis covered over by two of the wetable capillary sheets 53 and 54,respectively. Water from the reservoir 55 is fed gradually by the feedertube 56 which discharges underneath the bottom of the reservoir 55 andthe upper surface of the capillary sheet 53 upon which the reservoir 55rests whereby water is carried into the interface between the capillarysheet and the interface between the undersurface of the capillary sheet54 and the upper wettable surface of the upper tray 48 for spreading bycapillary action to the area of the upper capillary sheet 53 upon whichthe plant container 57 rests. FIG. 9 illustrates the optional employmentof a preformed wettable water absorptive sheet material 61 such as feltbetween the bottom of the plant container 57 and the upper surface ofthe capillary sheet 53 thereby facilitating capillary travel of waterinto the soil in the container 57 from the upper surface of thecapillary sheet 53. While the use of such a sheet of water absorptivematerial is within the practice of this invention, excellent results areobtained without it and usually it is not used.

Any excess of water from the reservoir 55 will drain through one or bothof the drain openings 52 and accumulates in the lower tray. In FIG. 9 analternative expedient is shown for accomplishing return flow bycapillary action from water in the lower tray to the capillary interfaceprovided by the capillary sheets 53 and 54 on the upper tray after flowfrom the reservoir 55 has ceased. According to this embodiment a portionof the drain opening 52 and of the surface of strip 51 that iscontinuous therewith is provided with a capillary silica and layer 58 byapplying a conventional adhesive that is sticky before drying iscomplete and applying to it while sticky a dusting of silica sand so asto adhere and provide a capillary surface essentially corresponding withthat of the silica sand catalyst sheet hereinabove mentioned. Thecapillary sand layer also is extended at 59 so as to underlie thecapillary sheet on the upper tray. While the capillary action of theadherent silica sand coating is utilized in one form of wicking materialby which return flow of water is accomplished from the lower tray to theinterface between the capillary sheets used to the interface between thelower capillary sheet and the surface of the upper tray, said interfacesare effective in obtaining continued travel by capillary action to anyarea of the uppermost capillary sheet that is under a plant containereven though the wettable surfaces presented at said interfaces aresubstantially smooth as contrasted with a surface such as silica sandthat in and of itself is effective to induce capillary travel. Thenumber of plant containers that may be supported by a given duplex trayis limited only by the relative dimensions of the tray and of thecontainer.

The water that is fed in for subirrigation may, if desired, have a smallamount of a plant nutrient therein. Alternatively, as illustrated inFIG. 9, particles 60 of slow release fertilizer may be distributed inappropriate amount in the capillary interface or interfaces provided bythe capillary sheet. They also may be employed in a similar manner inconnection with the other embodiments of this invention describedherein.

What is claimed is:
 1. In a method of irrigating with an aqueous liquidsoil within a plant container through an opening in the bottom thereofthat rests on a capillary sheet having capillary openings therein thatare about 0.045 to about 0.145 inch in diameter by capillary travelupwardly through said capillary openings and said opening in the bottomof said container, the improvement of which comprises feeding water intothe interface between an undersurface of said capillary sheet that iswettable and that is in face-to-face unbonded contacting relation withan essentially continuous and substantially smooth wettable uppersurface presented by a support bed for said plant container withattendant lateral spreading while confined in said interface to an areaof said capillary sheet underneath a plant container the bottom of whichis in contacting relation with the upper surface of said capillary sheetand with further travel through capillary openings in said area of thecapillary sheet and thence through said opening in the bottom of theplant container and into soil within the container.
 2. A methodaccording to claim 1 wherein said surface presented by said support bedis presented by a sheet of plastic that overlies a substantially rigidslab that is comprised in the support bed and that presents asubstantially flat upper surface.
 3. A method according to claim 1wherein the surface presented by said support bed is a substantiallyflat upper surface presented by a substantially rigid slab comprised inthe support bed.
 4. A method according to claim 1 wherein the capillarysheet is in the form of a plurality of unbonded contacting layers ofindividual capillary sheets.
 5. A method according to claim 1 whereinthe plant container presents a substantially flat bottom surface incontact with the capillary sheet.
 6. A method according to claim 5wherein at least 30% of the area of said flat bottom surface is open. 7.A method according to claim 1 wherein the upward travel of water fromthe upper surface of the capillary sheet through the opening in thebottom of the container is assisted by a wick that contacts said uppersurface of the capillary sheet and that traverses said opening in thebottom of the container and extends a substantial distance upwardly intosoil within the container.
 8. A method according to claim 7 wherein saidwick is in the form of a silica sand catalyst sheet the silica sandsurface of which is doubled or sanded on both sides for contact with theupper surface of the capillary sheet and soil in the container.
 9. Amethod according to claim 1 wherein the upward travel of water from theupper surface of the capillary sheet through the opening in the bottomof the container assisted by an interposed sheet of porous waterabsorptive material between the upper surface of the capillary sheet andthe bottom surface of the container.
 10. A method according to claim 1wherein plant nutrient is supplied by distributing a slow releasefertilizer in said interface for dissolution in water during its travelto soil in said container.
 11. In a soil irrigation system for supplyingan aqueous liquid to a plant rooted in soil in a container having anopening in its bottom which comprises a support bed for said containerpresenting a substantially flat wettable upper surface, a capillarysheet which has a wettable undersurface, which has a multiplicity ofcapillary openings therein from about 0.045 to about 0.145 inch indiameter, and which is spread over said surface presented by saidsupport bed in unbonded face-to-face contacting relation and means forfeeding water into the interface between the undersurface of saidcapillary sheet and said upper surface presented by said support bed,the improvement in that said surface that is presented by said supportbed and that is in face-to-face contacting relation with theundersurface of said capillary sheet is an essentially continuous andsubstantially smooth wetable surface.
 12. A soil irrigation systemaccording to claim 11 wherein said upper surface presented by saidsupport bed is the surface of an essentially continuous sheet ofwettable plastic that overlies and is supported by a substantially flatupper surface of a substantially rigid slab comprised in the supportbed.
 13. A soil irrigation system according to claim 11 wherein theessentially continuous and substantially smooth surface which ispresented by said support bed and with which the undersurface of thecapillary sheet is in face-to-face contact is the surface of asubstantially rigid slab comprised in the support bed.
 14. A soilirrigation system according to claim 11 wherein said capillary sheet isopaque.
 15. A soil irrigation system according to claim 11 wherein saidcapillary sheet is in the form of a plurality of unbonded contactinglayers of individual capillary sheets.
 16. A duplex supporting tray forsupporting plants growing in containers having a drain opening in thebottom thereof which comprises a first substantially horizontallydisposed and substantially rigid tray which is adapted to support one ormore of said containers thereon and which presents a substantiallysmooth and continuous flat upper surface that is wettable, a capillarysheet which has a multiplicity of capillary openings therein about 0.045to about 0.145 inch in diameter, the undersurface of which is wettableand is in face-to-face unbonded contact with said surface of said trayand which is disposed for making direct contact with the bottom of saidcontainer, a second substantially rigid tray disposed underneath saidfirst tray and adapted to contain therein a body of water, meansinterposed between said first and second trays for supporting said firsttray by said second tray with the underside of said first tray inproximate spaced relation to the upper surface of said second tray, andcapillary wick means for feeding water in said second tray into theinterface between the undersurface of said capillary sheet and the uppersurface presented by said first tray.
 17. A duplex tray according toclaim 16 which also comprises means for feeding water from a sourceother than water in said second tray into said interface and means fordraining liquid so fed into said interface from said inferface into saidsecond tray.
 18. A duplex tray according to claim 16 wherein said uppersurface presented by said first tray is the upper surface of anessentially continuous plastic sheet that is supported by said firsttray.
 19. A duplex tray according to claim 16 wherein said upper surfacepresented by said first tray is the surface of a substantially rigidslab that is comprised in said first tray.
 20. A duplex tray accordingto claim 16 wherein a portion of the second tray projects beyond aportion of the periphery of the first tray for enabling readyobservation of the presence of water in said second tray.
 21. A duplextray according to claim 16 wherein said capillary sheet is in the formof a plurality of unbonded contacting layers of individual capillarysheets.
 22. A soil irrigation system for supplying water to soil in acontainer for growing a plant by capillary travel upwardly into saidsoil through an opening in the bottom of said container which systemcomprises a support bed adapted to support one or more of saidcontainers that presents a substantially smooth and level waterimpervious wettable upper surface, a capillary sheet disposed inoverlying relation with respect to said surface the undersurface ofwhich is wettable and is in face-to-face unbonded relation with respectto said upper surface presented by said support bed and the uppersurface of which is disposed for making contact with a container placedthereon, means for feeding water into the interface between said surfaceand said capillary sheet, means for draining excess water from theregion of said interface and directing it into a reservoir situatedbelow the level of said support bed and means for removing water fromsaid reservoir and returning it into said interface, said capillarysheet having a multiplicity of substantially evenly spaced capillaryopenings therein that are essentially from about 0.05 to about 0.145inch in diameter.
 23. A soil irrigation system according to claim 22wherein said means for supplying water into said interface comprises asupply reservoir situated above the level of said support bed and meansfor directing water from said supply reservoir into said interface andwherein said means for removing water from said reservoir below thelevel of said support bed and returning it into said interface comprisesmeans for pumping water removed from said reservoir situated below thelevel of said support bed and directing the so pumped water into saidsupply reservoir.
 24. A soil irrigation system according to claim 22wherein said means for removing water from said reservoir and returningit to said interface comprises wick means extending from adjacent thebottom of said reservoir into the region of said interface.